<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2013</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>erl_prim_loader</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
<file>erl_prim_loader.xml</file>
</header>
<module>erl_prim_loader</module>
<modulesummary>Low Level Erlang Loader</modulesummary>
<description>
<p><c>erl_prim_loader</c> is used to load all Erlang modules into
the system. The start script is also fetched with this low level
loader.</p>
<p><c>erl_prim_loader</c> knows about the environment and how to
fetch modules. The loader could, for example, fetch files using
the file system (with absolute file names as input), or a
database (where the binary format of a module is stored).</p>
<p>The <c>-loader Loader</c> command line flag can be used to
choose the method used by the <c>erl_prim_loader</c>. Two
<c>Loader</c> methods are supported by the Erlang runtime system:
<c>efile</c> and <c>inet</c>. If another loader is required, then
it has to be implemented by the user. The <c>Loader</c> provided
by the user must fulfill the protocol defined below, and it is
started with the <c>erl_prim_loader</c> by evaluating
<c>open_port({spawn,Loader},[binary])</c>.</p>
<warning><p>The support for loading of code from archive files is
experimental. The sole purpose of releasing it before it is ready
is to obtain early feedback. The file format, semantics,
interfaces etc. may be changed in a future release. The functions
<c>list_dir/1</c> and <c>read_file_info/1</c> as well as the flag
<c>-loader_debug</c> are also experimental</p></warning>
</description>
<datatypes>
<datatype>
<name name="host"/>
</datatype>
</datatypes>
<funcs>
<func>
<name name="start" arity="3"/>
<fsummary>Start the Erlang low level loader</fsummary>
<desc>
<p>Starts the Erlang low level loader. This function is called
by the <c>init</c> process (and module). The <c>init</c>
process reads the command line flags <c>-id <anno>Id</anno></c>,
<c>-loader <anno>Loader</anno></c>, and <c>-hosts <anno>Hosts</anno></c>. These are
the arguments supplied to the <c>start/3</c> function.</p>
<p>If <c>-loader</c> is not given, the default loader is
<c>efile</c> which tells the system to read from the file
system.</p>
<p>If <c>-loader</c> is <c>inet</c>, the <c>-id <anno>Id</anno></c>,
<c>-hosts <anno>Hosts</anno></c>, and <c>-setcookie Cookie</c> flags must
also be supplied. <c><anno>Hosts</anno></c> identifies hosts which this
node can contact in order to load modules. One Erlang
runtime system with a <c>erl_boot_server</c> process must be
started on each of hosts given in <c><anno>Hosts</anno></c> in order to
answer the requests. See <seealso
marker="kernel:erl_boot_server">erl_boot_server(3)</seealso>.</p>
<p>If <c>-loader</c> is something else, the given port program
is started. The port program is supposed to follow
the protocol specified below.</p>
</desc>
</func>
<func>
<name name="get_file" arity="1"/>
<fsummary>Get a file</fsummary>
<desc>
<p>This function fetches a file using the low level loader.
<c><anno>Filename</anno></c> is either an absolute file name or just the name
of the file, for example <c>"lists.beam"</c>. If an internal
path is set to the loader, this path is used to find the file.
If a user supplied loader is used, the path can be stripped
off if it is obsolete, and the loader does not use a path.
<c><anno>FullName</anno></c> is the complete name of the fetched file.
<c><anno>Bin</anno></c> is the contents of the file as a binary.</p>
<p>The <c><anno>Filename</anno></c> can also be a file in an archive. For example
<c>$OTPROOT/lib/</c><c>mnesia-4.4.7.ez/mnesia-4.4.7/ebin/</c><c>mnesia.beam</c>.
See <seealso marker="kernel:code">code(3)</seealso> about archive files.</p>
</desc>
</func>
<func>
<name name="get_path" arity="0"/>
<fsummary>Get the path set in the loader</fsummary>
<desc>
<p>This function gets the path set in the loader. The path is
set by the <c>init</c> process according to information found
in the start script.</p>
</desc>
</func>
<func>
<name name="list_dir" arity="1"/>
<fsummary>List files in a directory</fsummary>
<desc>
<p>Lists all the files in a directory. Returns
<c>{ok, <anno>Filenames</anno>}</c> if successful. Otherwise, it returns
<c>error</c>. <c><anno>Filenames</anno></c> is a list of
the names of all the files in the directory. The names are
not sorted.</p>
<p>The <c><anno>Dir</anno></c> can also be a directory in an archive. For example
<c>$OTPROOT/lib/</c><c>mnesia-4.4.7.ez/mnesia-4.4.7/ebin</c>.
See <seealso marker="kernel:code">code(3)</seealso> about archive files.</p>
</desc>
</func>
<func>
<name name="read_file_info" arity="1"/>
<fsummary>Get information about a file</fsummary>
<desc>
<p>Retrieves information about a file. Returns
<c>{ok, <anno>FileInfo</anno>}</c> if successful, otherwise
<c>error</c>. <c><anno>FileInfo</anno></c> is a record
<c>file_info</c>, defined in the Kernel include file
<c>file.hrl</c>. Include the following directive in the module
from which the function is called:</p>
<code type="none">
-include_lib("kernel/include/file.hrl").</code>
<p>See <seealso marker="kernel:file">file(3)</seealso> for more info about
the record <c>file_info</c>.</p>
<p>The <c><anno>Filename</anno></c> can also be a file in an archive. For example
<c>$OTPROOT/lib/</c><c>mnesia-4.4.7.ez/mnesia-4.4.7/ebin/</c><c>mnesia</c>.
See <seealso marker="kernel:code">code(3)</seealso> about archive files.</p>
</desc>
</func>
<func>
<name name="read_link_info" arity="1"/>
<fsummary>Get information about a link or file</fsummary>
<desc>
<p>This function works like
<seealso marker="#read_file_info/1">read_file_info/1</seealso>
except that if <c><anno>Filename</anno></c> is a symbolic link,
information about the link will be returned in the <c>file_info</c>
record and the <c>type</c> field of the record will be set to
<c>symlink</c>.</p>
<p>If <c><anno>Filename</anno></c> is not a symbolic link, this function
returns exactly the same result as <c>read_file_info/1</c>.
On platforms that do not support symbolic links, this function
is always equivalent to <c>read_file_info/1</c>.</p>
</desc>
</func>
<func>
<name name="set_path" arity="1"/>
<fsummary>Set the path of the loader</fsummary>
<desc>
<p>This function sets the path of the loader if <c>init</c>
interprets a <c>path</c> command in the start script.</p>
</desc>
</func>
</funcs>
<section>
<title>Protocol</title>
<p>The following protocol must be followed if a user provided
loader port program is used. The <c>Loader</c> port program is
started with the command
<c>open_port({spawn,Loader},[binary])</c>. The protocol is as
follows:</p>
<pre>
Function Send Receive
-------------------------------------------------------------
get_file [102 | FileName] [121 | BinaryFile] (on success)
[122] (failure)
stop eof terminate</pre>
</section>
<section>
<title>Command Line Flags</title>
<p>The <c>erl_prim_loader</c> module interprets the following
command line flags:</p>
<taglist>
<tag><c>-loader Loader</c></tag>
<item>
<p>Specifies the name of the loader used by
<c>erl_prim_loader</c>. <c>Loader</c> can be <c>efile</c>
(use the local file system), or <c>inet</c> (load using
the <c>boot_server</c> on another Erlang node). If
<c>Loader</c> is user defined, the defined <c>Loader</c> port
program is started.</p>
<p>If the <c>-loader</c> flag is omitted, it defaults to
<c>efile</c>.</p>
</item>
<tag><c>-loader_debug</c></tag>
<item>
<p>Makes the <c>efile</c> loader write some debug information,
such as the reason for failures, while it handles files.</p>
</item>
<tag><c>-hosts Hosts</c></tag>
<item>
<p>Specifies which other Erlang nodes the <c>inet</c> loader
can use. This flag is mandatory if the <c>-loader inet</c>
flag is present. On each host, there must be on Erlang node
with the <c>erl_boot_server</c> which handles the load
requests. <c>Hosts</c> is a list of IP addresses (hostnames
are not acceptable).</p>
</item>
<tag><c>-id Id</c></tag>
<item>
<p>Specifies the identity of the Erlang runtime system. If
the system runs as a distributed node, <c>Id</c> must be
identical to the name supplied with the <c>-sname</c> or
<c>-name</c> distribution flags.</p>
</item>
<tag><c>-setcookie Cookie</c></tag>
<item>
<p>Specifies the cookie of the Erlang runtime system. This flag
is mandatory if the <c>-loader inet</c> flag is present.</p>
</item>
</taglist>
</section>
<section>
<title>SEE ALSO</title>
<p><seealso marker="init">init(3)</seealso>,
<seealso marker="kernel:erl_boot_server">erl_boot_server(3)</seealso></p>
</section>
</erlref>
